Method of producing pulp moldings

ABSTRACT

A method of producing pulp moldings having a paper-making process comprising the steps of assembling split mold halves ( 11, 12 ) having suction passageways ( 14 ) to form a paper-making mold ( 10 ), feeding pulp slurry of predetermined set feed concentration into the cavity ( 13 ) in the paper-making mold ( 10 ), and sucking the pulp slurry through the suction passageways ( 14 ) to form a pulp layer ( 15 ) on the inner surface of the paper-making mold ( 10 ), wherein the concentration of the pulp slurry in the cavity ( 13 ) in the initial and/or final period of formation of the pulp layer ( 15 ) in the paper-making process is lower than the above-mentioned set feed concentration of the pulp slurry.

TECHNICAL FIELD

[0001] The present invention relates to a method of producing a pulpmolded article.

BACKGROUND ART

[0002] There is a method of producing pulp molded articles whichinvolves a papermaking step comprising feeding a pulp slurry to thecavity of a papermaking mold composed of splits each having suctionpassageways, and sucking the pulp slurry through the suction passagewaysto form a pulp layer on the inner side of the papermaking mold. In thepapermaking step of this method, when the cavity is not full of the pulpslurry in the initial stage of pulp slurry feeding or after the end ofthe feeding, the solid component of the pulp slurry such as pulp tendsto sink spontaneously due to the insufficient effect of agitation thanin the stage where the cavity is sufficiently filled with the pulpslurry and the pulp slurry is sucked through the suction passageways forpapermaking. When pulp is sinking, the water content is sucked moreeasily so that the slurry concentration increases. As a result, there isa tendency that a resulting molded article has a larger thickness in itslower part than in the upper part. The tendency is particularlyconspicuous in making hollow molded articles the body of which steeplyrises from the bottom, such as bottles and cartons. This has been one ofthe problems in manufacturing of hollow molded articles.

[0003] Accordingly, an object of the present invention is to provide amethod of producing a pulp molded article having reduced thicknessunevenness in the vertical direction.

DISCLOSURE OF THE INVENTION

[0004] The present inventors have found that the thickness unevenness inthe vertical direction of a molded article can be reduced by dilutingthe pulp slurry in the cavity in the initial stage and/or the finalstage of pulp layer formation in the papermaking step.

[0005] The present invention has been completed based on this finding.That is, the above object is accomplished by providing a method ofproducing a pulp molded article which includes a papermaking stepcomprising joining splits each having suction passageways into apapermaking mold, feeding a pulp slurry into the cavity of thepapermaking mold, and sucking the pulp slurry through the suctionpassageways to form a pulp layer on the inner surface of the papermakingmold, wherein a fluid for diluting the pulp slurry is fed into thecavity during the pulp slurry is remaining in the cavity, and theconcentration of the pulp slurry in the cavity in the final stage ofpulp layer formation in the papermaking step is lowered.

[0006] The present invention also accomplishes the above object byproviding a method of producing a pulp molded article which includes apapermaking step comprising joining splits each having suctionpassageways into a papermaking mold, feeding a pulp slurry into thecavity of the papermaking mold, and sucking the pulp slurry through thesuction passageways to form a pulp layer on the inner surface of thepapermaking mold, wherein at least two pulp slurries of differentcomposition are fed into the cavity, the start of feeding the first pulpslurry of said pulp slurries is followed by feeding the second pulpslurry of said pulp slurries, and a fluid for dilution and agitation isfed into the cavity at least the final pulp slurry of said pulp slurriesfed into the cavity is remaining in the cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 schematically illustrates a papermaking mold and a pulpslurry feed system use in the papermaking step of the method forproducing a molded article according to the present invention.

[0008] FIGS. 2(a) through (g) show a schematic flow of an embodiment ofthe method for producing a pulp molded article according to the presentinvention, and FIG. 2(h) is a schematic of the resulting pulp moldedarticle.

[0009]FIG. 3 is a schematic showing a multilayer structure of a moldedarticle produced by the present invention.

[0010]FIG. 4 is a schematic (corresponding to FIG. 3) showing othermultilayer structures of a molded article produced by the presentinvention.

[0011]FIG. 5 is a schematic chart of the papermaking step in timesequence in Examples of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0012] The method of producing a pulp molded article (hereinafter simplyreferred to as a molded article) according to the present invention willbe described based on its preferred embodiment with reference to theaccompanying drawings.

[0013]FIG. 1 schematically illustrates a papermaking mold and a pulpslurry feed system use in the papermaking step of an embodiment of themethod for producing a molded article according to the presentinvention. In the Figure, the papermaking mold is a split mold.

[0014] In this embodiment two pulp slurries having differentcompositions as described below are used to manufacture a moldedarticle. As shown in FIG. 1, the pulp slurry feed system includes twopipe lines A and B for feeding the pulp slurry and also a pipe line Cwhich is for feeding a fluid for pulp slurry dilution described later(hereinafter also referred to as a diluting fluid). The feed system isdesigned to feed these three kinds of fluids from a common pipe line Dthrough the opening of the papermaking mold. V1 to V4 shown in FIG. 1are valves. The system also has a pipe line E for feeding air or steaminto the cavity in dewatering. The splits 11 each have a plurality ofsuction passageways 14. The inner surface of each split 11 is coveredwith a papermaking screen (not shown) having a prescribed opening size.

[0015] FIGS. 2(a) to (g) show the flow of the method for producing amolded article according to this embodiment. (a) is the step ofinjecting a diluting fluid. (b) is the step of injecting a first pulpslurry and dewatering. (c) is the step of dewatering the first pulpslurry and injecting a second pulp slurry. (d) is the step of dewateringthe second pulp slurry and injecting water after the injection of thesecond pulp slurry. (e) is the step of inserting a pressing member. (f)is the step of pressing and dewatering. (g) is the step of removal fromthe mold.

[0016] In the initial stage of pulp layer formation in the papermakingstep, the concentration of the pulp slurry in the cavity C is made lowerthan the predetermined concentration of the first pulp slurry to be fed.In the present embodiment, in particular, the concentration of the pulpslurry in the cavity C is made lower than the predeterminedconcentration of the first pulp slurry while the liquid level in thecavity C is rising in order to reduce thickness unevenness that mayoccur in the vertical direction in the initial stage of pulp layerformation.

[0017] In the present embodiment, the valves V1 to V4 are operated so asto feed only the diluting fluid from the line C of FIG. 1. Then, asshown in FIG. 2(a), the diluting fluid W is injected, i.e., poured underpressure into the cavity 13 through the upper opening of the papermakingmold 10, which is composed of a pair of splits 11 and 12 butted togetherto form the cavity 13 whose shape agrees with the contour of a moldedarticle to be produced. The diluting fluid W is injected by means of,for example, a pump. The injection pressure of the diluting fluid ispreferably 0.01 to 5 MPa, more preferably 0.01 to 3 MPa.

[0018] Water is preferably used as the diluting fluid for improved outerappearance of molded articles and easiness of pipe cleaning. Warm watermay be used to increase dewatering efficiency. In using warm water, thewater temperature is preferably 35 to 90° C., more preferably 45 to 80°C.

[0019] It is preferable to use, as a diluting fluid, white water drainedfrom the previously fed pulp slurry, which will reduce the amount offresh water to be used and the amount of waste liquid.

[0020] A pulp slurry which is adjusted low concentration in advance canalso be used as the diluting fluid. In this case, the concentration ofthe pulp slurry as a diluting fluid is preferably 50% or less of that ofthe pulp slurry fed (predetermined concentration) and is more preferably1% by weight or less. It is preferred that the concentration of the pulpslurry as a diluting fluid be lowered as the concentration of the pulpslurry to be fed increases.

[0021] A detergent or various functionalizing additives may be added inthe diluting fluid.

[0022] The injection volume of the diluting fluid is decided inconsideration of the size and the shape of a molded article to beproduced (or the cavity volume) and the the first pulp slurry with thepredetermined concentration is fed. Where the predeterminedconcentration of the first pulp slurry is 1% by weight or higher, apreferred injection volume Vw of the diluting fluid is in the range(¼)ρs·Vc<Vw<8Vc. The range is calculated from the length of the dilutingfluid feed pipe line having the three valves as shown in FIG. 1 and thecavity volume. If the injection volume Vw of the diluting fluid is(¼)ρs·Vc or less, the largest thickness to smallest thickness ratio of amolded article would exceed a preferred range of from 1.0 to 3.0, i.e.,the pulp layer would suffer from considerable unevenness thickness. Inthis case, the pulp layer may be scorched in drying process, the dryingefficiency is reduced, or the resulting molded article has reducedcompressive strength. If the injection volume Vw of the diluting fluidis 8 or more times the cavity volume Vc, a long time is required on tofinish of papermaking process. In the above relationship, ρs is thepredetermined concentration (wt %) of the pulp slurry feed, Vc is thevolume of the cavity; and Vw is the injection volume of the dilutingfluid. More concretely, for instance, the concentration ρs of the pulpslurry in the cavity before pouring water as a diluting fluid is 2% byweight, and the cavity volume Vc is 1 liter, the injection volume ofwater Vw is preferably in the range 0.5<Vw<8 liters.

[0023] After a predetermined amount of the diluting fluid W is injected,the valves V1 and V2 are operated so that only a first pulp slurry I maybe fed from the line A of FIG. 1. As shown in FIG. 2(b), the first pulpslurry I is injected to a certain liquid level in the cavity 13. In thepresent embodiment, since the diluting liquid is supplied before thefeed of the first pulp slurry I, the pulp slurry in the cavity 13 is adiluted one. Injection of the first pulp slurry I is performed with, forexample, a pump. The injection pressure of the first pulp slurry I ispreferably 0.01 to 5 MPa, more preferably 0.01 to 3 MPa.

[0024] It is preferable that the first pulp slurry I is injected in thecavity after the supply of the diluting fluid, however, the first pulpslurry I may be injected during, simultaneously with, or before thesupply of the diluting fluid by operation of the valve VI. In case ofafter or simultaneous injection of the first pulp slurry I, the dilutingfluid serves as a fluid for dilution and agitation.

[0025] The predetermined concentration of the first pulp slurry ispreferably 0.1 to 6% by weight, more preferably 0.5 to 3% by weight. Ata concentration lower than 0.1% by weight, cases sometimes result inwhich a uniform thickness is not obtained only to provide a rejectivemolded article. At a concentration of higher than 6% by weight, anincreased amount of the diluting fluid would be required to obtain adesired effect of diluting the pulp slurry in the cavity, which needs anincreased time for injecting the diluting fluid. A predeterminedconcentration of 0.5% by weight or higher is particularly effective tostabilize molding properties, and a predetermined concentration of 3% byweight or lower is particularly effective to level the thicknessvariation in the vertical direction.

[0026] The pulp fiber which can be used in the first pulp slurryincludes any kinds that are used in this type of pulp molded articles.In particular, use of specific pulp fiber as described later providesmolded articles with specific characteristics described later. The firstpulp slurry may contain, in addition to the pulp fiber and water, othercomponents, such as inorganic substances, e.g., talc and kaolinite,inorganic fibers, e.g., glass fiber and carbon fiber, powdered orfibrous thermoplastic synthetic resins, e.g., polyolefins, non-wood orplant fiber, polysaccharides, and so forth. The amount of these othercomponents is preferably 1 to 70% by weight, particularly 5 to 50% byweight, based on the total amount of the pulp fiber and the othercomponents.

[0027] As stated above, in the present embodiment of the method ofproducing a pulp molded article, the pulp slurry concentration in thecavity in the initial stage of pulp layer formation in the papermakingstep is lower than the predetermined concentration of the first pulpslurry feed. The term “initial stage” of pulp layer formation in thepapermaking step denotes the stage in which the proportion of pulphaving been supplied to the cavity is from 0 to 30%, preferably 0 to20%, of the total pulp necessary for completion of a pulp moldedarticle.

[0028] According to the present embodiment of the method of producing apulp molded article, the pulp slurry concentration in the cavity in theinitial stage of pulp layer formation in the papermaking step is lowerthan the predetermined concentration of the first pulp slurry feed.Where, in particular, the predetermined concentration of the first pulpslurry feed is 1% by weight or higher, the pulp slurry concentration ρcin the cavity in the initial stage of pulp layer formation in thepapermaking step [ρc=amount of pulp in the cavity/(water content of theslurry in the cavity+water content of the diluting fluid in the cavity)]preferably ranges from 16 to [2500/(25+6ρs)]% of the predeterminedconcentration of the first pulp slurry. The upper limit of the pulpslurry concentration ρc in the above range is the one calculated basedon the injection volume Vw of the diluting fluid [(¼)ρs·Vs].

[0029] Where the pulp slurry concentration ρc in the cavity is less than16%, the largest thickness to smallest thickness ratio (the largestthickness/the smallest thickness) of a molded article would exceed apreferred range of from 1.0 to 3.0. In this case, the pulp layer wouldsuffer from considerable thickness unevenness. It may follow that thepulp layer is scorched on drying, the drying efficiency is reduced, orthe resulting molded article has reduced compressive strength. Where theρc exceeds [2500/(25+6ρs)]%, the requisite injection volume Vw of thediluting fluid is 8 or more times the cavity volume Vc, and the timerequired for the papermaking step becomes long.

[0030] After the first pulp slurry I is injected until the amount of theslurry in the cavity 13 reaches a prescribed amount, dewatering bysuction of the pulp slurry through the suction passageways 14 isstarted. The water content in the first pulp slurry of low concentrationis thus discharged out of the papermaking mold 10, and the pulp fiber isdeposited on the inner surface of the cavity 13 (i.e., in the inner sideof the papermaking screen) to form a first pulp layer 15 as an outermostlayer as shown in FIG. 2(b). Since a predetermined pressure is appliedto the first pulp slurry I of low concentration in the cavity 13 asmentioned above, dewatering through the suction passageways 14 proceedssmoothly, and the pulp fiber is uniformly deposited without thicknessunevenness in the vertical direction while being prevented from settlingspontaneously. Because the first pulp slurry I is continuously injectedwhile the slurry is sucked through the suction passageways 14, theslurry concentration in the cavity 13 gradually increases over that atthe start of pulp layer formation.

[0031] After a predetermined amount of the first pulp slurry I has beeninjected, the valves V1 and V2 are operated so that only a second slurrymay be fed from the line B of FIG. 1, and a second pulp slurry IIdifferent from the first pulp slurry I in composition is injected underpressure into the cavity 13 through the upper opening of the papermakingmold 10 as shown in FIG. 2(c). As a result, there is a mixed slurry ofthe first pulp slurry and the second pulp slurry in the cavity 13. Theinjection pressure of the second pulp slurry II can be about the same asthat of the first pulp slurry I. By the injection of the second pulpslurry, the pressure in the cavity 13 is maintained.

[0032] The second pulp slurry is not particularly limited inconcentration as long as it has a different composition from the firstone's. Similarly to the first pulp slurry, a preferred concentration is0.1 to 6% by weight, particularly 0.5 to 3% by weight. At aconcentration lower than 0.1% by weight, the pulp slurry can fail toprovide a uniform thickness, resulting in unsatisfactory molding. A pulpslurry having a concentration higher than 6% by weight will need anincreased amount of a diluting fluid to obtain a desired effect indiluting the pulp slurry in the cavity, which needs an increased timefor injecting the diluting fluid.

[0033] The pulp fiber which can be used in the second pulp slurryincludes any kinds that are used in this type of pulp molded articles.In particular, use of specific pulp fiber as described later providesmolded articles with specific characteristics described later. Thesecond pulp slurry may contain, in addition to the pulp fiber and water,other components, such as inorganic substances, e.g., talc andkaolinite, inorganic fibers, e.g., glass fiber and carbon fiber,powdered or fibrous thermoplastic synthetic resins, e.g., polyolefins,non-wood or plant fiber, polysaccharides, and so forth. The amount ofthese other components is preferably 1 to 70% by weight, particularly 5to 50% by weight, based on the total amount of the pulp fiber and theother components.

[0034] While the second pulp slurry is being injected, the cavity 13 iscontinuously dewatered by suction through the suction passageways 14,whereby a mixed pulp layer (not shown), which is composed of thecomponents of the mixed slurry, is formed on the first pulp layer 15.Since the proportion of the second pulp slurry to the first pulp slurryin the mixed slurry increases continuously with time, the composition ofthe mixed layer formed on the first pulp layer 15 varies continuouslyfrom the composition of the first pulp slurry to that of the second pulpslurry. Since the cavity 13 is in a pressurized state, the mixed layeris formed with a uniform thickness. In detail, because each pulp slurryis fed under pressure into the cavity 13, a convection flow is generatedin the cavity 13 to agitate the pulp slurry even in the production of athree-dimensional hollow molded article with its body steeply upstandingfrom the bottom as in the present embodiment. Therefore, the pulp slurryconcentration is equalized in the vertical direction of the cavity 13 tothereby form the first pulp layer 15, the mixed layer 16, and a secondpulp layer 17 each with a uniform thickness.

[0035] Then, the concentration of the pulp slurry in the cavity 13 ismade lower than the predetermined concentration of the second pulpslurry in the final stage of second pulp layer 17 formation in thepapermaking step. In the present embodiment, in particular, theconcentration of the pulp slurry in the cavity C is made lower than thepredetermined concentration of the second pulp slurry while the liquidlevel in the cavity C is falling in order to effectively reducethickness unevenness in the vertical direction in the final stage ofsecond pulp layer formation thereby providing a uniform thickness.

[0036] According to the present embodiment, before injection of apredetermined amount of the second pulp slurry II comes to an end, thevalve V1 is operated so that a diluting fluid (fluid for dilution andagitation) may be fed from the line C of FIG. 1, and the diluting fluidis fed under pressure together with the second pulp slurry II so thatthe pulp slurry concentration in the cavity 13 in the final stage of thesecond pulp layer formation in the papermaking step is lower than thepredetermined concentration of the second pulp slurry.

[0037] On completing injection of a predetermined amount of the secondpulp slurry II, V1 is operated so that only the diluting fluid may befed from the line C, and only the diluting fluid continues beinginjected as shown in FIG. 2(d) to lower the pulp slurry concentration inthe cavity 13 than the predetermined concentration of the second pulpslurry in the final stage of second pulp layer formation in thepapermaking step. The second pulp slurry remaining in the cavity 13 isthus diluted and agitated by feeding the diluting fluid, andcontinuation of dewatering through the suction passageways 14 results inuniform formation of the second pulp layer 17, an innermost layer, as adeposit of the component of the second pulp slurry, on the mixed layer.In this case, too, since the pulp slurry in the cavity 13 is beingdiluted and agitated by the injected diluting fluid, the second pulplayer 17 is formed with a uniform thickness. Further, since the dilutingfluid is fed under pressure, dewatering through the suction passageways14 proceeds satisfactorily to give a satisfactory finish to the innerside.

[0038] According to the present embodiment, in particular, water, warmwater, etc. injected as a diluting fluid also serves to wash away thesecond pulp slurry remaining in the pipe line. As a result, when apapermaking is started again from scratch, only the first pulp slurrycan be fed, and deposition of the second pulp on the outer surface of amolded article is avoided.

[0039] It is possible to start injection of the diluting fluid aftercompletion of the injection of the second pulp slurry II while thesecond pulp slurry remains in the cavity.

[0040] As described above, in the production of a pulp molded articleaccording to the present embodiment, the pulp slurry concentration inthe cavity is made lower than the predetermined concentration of thesecond pulp slurry in the final stage of pulp layer formation in thepapermaking step. The term “final stage” of pulp layer formation in thepapermaking step denotes the stage in which the proportion of pulphaving been fed into the cavity is from 70 to 100%, preferably 80 to100%, of the total pulp fibers necessary to complete a pulp moldedarticle.

[0041] In the production of a pulp molded article according to thepresent embodiment, the pulp slurry concentration in the cavity in thefinal stage of pulp layer formation in the papermaking step ispreferably 16 to 18% of the predetermined concentration of the secondpulp slurry.

[0042] The volume of the diluting fluid to be injected in the finalstage of pulp layer formation is decided appropriately according to thesize and the shape of a molded article to be produced (or the cavityvolume) and the predetermined concentration of the second pulp slurry.Where the predetermined concentration of the second pulp slurry is 1% byweight or higher, a preferred injection volume Vw of the diluting fluidis in the range (¼)ρs·Vc<Vw<8Vc. If the injection volume Vw of thediluting fluid is (¼)ρs·Vc or less, the largest thickness to smallestthickness ratio (the largest thickness/the smallest thickness) of amolded article would exceed a preferred range of from 1.0 to 3.0, i.e.,the pulp layer would suffer from considerable thickness unevenness. Itmay follow that the pulp layer is scorched on drying, the dryingefficiency is reduced, or the resulting molded article has reducedcompressive strength. If the injection volume Vw of the diluting fluidis 8 or more times the cavity volume Vc, a long time is required forcompletion of papermaking step.

[0043] On forming a prescribed pulp layer, injection of the dilutingfluid is stopped, and dewatering is performed. In the step of dewateringas shown in FIG. 2(e), a hollow, elastically stretchable pressing member18 is inserted into the cavity 13 while the cavity 13 is in suction. Thepressing member 18 is used in its inflated state in the cavity 13 like aballoon to press the laminate consisting of the first pulp layer 15, themixed layer 16, and the second pulp layer 17 (hereinafter referred to asa pulp preform) onto the inner surface of the cavity 13 thereby totransfer the inside profile of the cavity 13 to the preform.Accordingly, the pressing member 18 is made of urethane, fluororubber,silicone rubber, elastomers, etc., which are excellent in tensilestrength, impact resilience, and stretchability.

[0044] A pressurizing fluid is then fed into the pressing member 18 toexpand it as shown in FIG. 2(f). The pulp preform is thus pressed towardthe inner wall of the cavity 13 by the expanded pressing member 18. Asthe pulp preform is pressed to the inner wall of the cavity 13 by theexpanded pressing member 18, the inside profile of the cavity 13 istransferred to the pulp preform and, at the same time, dewateringproceeds further. Since the pulp preform is pressed from its insideagainst the inner wall of the cavity 13, the inner profile of the cavity13 is transferred to the pulp preform with good precision howevercomplicated the inner profile may be. Besides, because there is no stepof coupling separately formed parts unlike a conventional method ofproducing pulp moldings, the resulting molded article has no seams northick-walled parts due to coupling. As a result, the resulting moldedarticle has secured strength and a satisfactory appearance. Thepressurizing fluid for expanding the pressing member 18 includescompressed air (heated air), oil (heated oil) and other liquids. Thepressure for feeding the pressurizing fluid is preferably 0.01 to 5 MPa,particularly 0.1 to 3 MPa.

[0045] After the profile of the inner wall of the cavity 13 issufficiently transferred to the pulp preform, and the pulp preform isdewatered up to a prescribed water content, the pressurizing fluid iswithdrawn from the pressing member 18 as shown in FIG. 2(g), whereuponthe pressing member 18 shrinks automatically to its original size. Theshrunken pressing member 18 is taken out of the cavity 13, and thepapermaking mold 10 is opened to remove the wet pulp preform 19 havingthe prescribed water content.

[0046] The pulp preform 19 is then subjected to the step of heat drying.In the heat drying step, the same operation as in the papermaking stepshown in FIG. 2 is conducted, except that papermaking and dewatering arenot carried out. Firstly, a heating mold, which is a set of splitsjoined together to form a cavity in conformity to the outer contour of amolded article to be produced, is heated to a prescribed temperature,and the wet pulp preform is fitted therein.

[0047] Secondly, a pressing member similar to the pressing member 18used in the papermaking step is put into the pulp preform, and apressurizing fluid is fed into the pressing member to expand it, wherebythe pulp preform is pressed onto the inner wall of the cavity by theexpanded pressing member. The material of the pressing member and thepressure for feeding the pressurizing fluid can be the same as thoseused in the papermaking step. In this state, the pulp preform is driedby the heat. After the pulp preform dries sufficiently, the pressurizingfluid is withdrawn from the pressing member, and the shrunken pressingmember is taken out. The heating mold is opened to remove the resultingmolded article.

[0048] In the present embodiment, a diluting fluid is injected into thecavity in the initial stage and the final stage of pulp layer formation,particularly while the amount of the pulp slurry is increasing in theinitial stage and while it is decreasing in the final stage, to lowerthe pulp slurry concentration in the cavity than the predeterminedconcentration of the first or the second pulp slurry. As a result, thesolid ingredients in the slurry do not precipitate and a molded articlefree from vertical unevenness in thickness can be formed. Since thefirst pulp slurry I and the second pulp slurry II are fed into thecavity 13 in a continuous manner, a molded article having a multilayerstructure in its thickness direction can be produced efficiently. Wherewater is injected as a diluting liquid after completion of injection ofthe second pulp slurry, the second pulp slurry is expelled by the waterfrom the line D of FIG. 1. Therefore, when a next molding cycle iscommenced, a papermaking operation can be started immediately.

[0049] As depicted in FIG. 2(h), the molded article 1 thus produced is acylindrical bottle (hollow container) having a smaller diameter in theopening 2 than in the body 3, which is especially suited to hold powder,particles, etc. The molded article 1 is an integrally molded shape withno seams on any of the opening 2, the body 3, and the bottom 4 and thusexhibits increased strength and a satisfactory outer appearance.

[0050] The multilayer structure of the molded article produced by thepresent embodiment is as shown in FIG. 3. Between the first pulp layer15 as an outermost layer and the second pulp layer 17 as an innermostlayer, there is formed the mixed layer 16 of which the compositionvaries continuously from the composition of the first pulp layer to thatof the second pulp layer. The mixed layer 16 provides increased adhesivestrength between the first pulp layer 15 and the second pulp layer 17,with which separation of these two layers is effectively prevented.Formation of the mixed layer 16 between the first pulp layer 15 and thesecond pulp layer 17 can be confirmed by observation of microscope.

[0051] Each thickness of the first pulp layer 15, the mixed layer 16,and the second pulp layer 17 is decided appropriately according to theuse of the molded article. It is preferred for the outermost layer (thefirst pulp layer 15 in the present embodiment) to have a thickness of 5to 90%, particularly 10 to 70%, especially 10 to 50%, of the totalthickness of the molded article. With this outer layer thickness range,sufficient hiding capabilities are exhibited when seen from the outsideeven where the inner layer is made of pulp fiber of low whiteness; theinner layer is hardly exposed even where the outermost layer isscratched; and the inner layer exhibits sufficient properties ofcovering the inside of the molded article. The thickness of each layerdepends on the amounts and the concentrations of the first and secondpulp slurries.

[0052] Having the multilayer structure, the individual layers can havedifferent functions. For example, only the first pulp layer 15 as theoutermost layer can be rendered colored by incorporating a colorant,such as a pigment or a dye, or colored traditional Japanese paper or acolored synthetic fiber into the first pulp slurry. Incorporating thecolorant only into the first pulp slurry is advantageous in that thetone of that slurry can be adjusted with ease in case where pulp havinga relatively low whiteness, for example, pulp obtained from used paper,such as de-inked pulp, is compounded into the first pulp slurry (e.g.,to a whiteness of 60% or more, particularly 70% or more). The amount ofthe colorant to be added is preferably 0.1 to 15% by weight based on thepulp fiber.

[0053] The first or the second pulp slurry can contain pulp fiber havinga weighted-average fiber length of 0.8 to 2.0 mm, a Canadian StandardFreeness of 100 to 600 cc, and such distribution of fiber length ascomprises 20 to 90%, based on the total fiber, of fibers whose lengthranges from 0.4 mm to 1.4 mm and 5 to 50%, based on the total fiber, offibers whose length is longer than 1.4 mm and not longer than 3.0 mm. Inthis case, the first pulp layer 15 or the second pulp layer 17 will havean extremely uniform thickness. Particularly where the first pulp slurrycontains hard wood bleached pulp (LBKP) and comprises pulp fiber havinga weighted-average fiber length of 0.2 to 1.0 mm) a Canadian StandardFreeness of 50 to 600 cc, and such a distribution of fiber length ascomprises 50 to 95%, based on the total fiber, of fibers whose lengthranges from 0.4 mm to 1.4 mm, the resulting molded article will haveimproved surface smoothness and suitability to printing or coating.

[0054] The term “weighted-average fiber length” as used herein is avalue obtained by measuring a distribution of pulp fiber length andcalculating a weighted average from the distribution. Measurement wasmade with a fiber length analyzer Kajaani FS-200 (manufactured by ValmetAutomation Company). The fiber count was set at 20,000 or more.

[0055] Incorporating additives, such as water-proofing agents, waterrepellents, vapor-proofing agents, fixing agents, antifungal agents,antistatic agents, and the like, into the first pulp slurry imparts therespective functions to the first pulp layer 15. It is preferred for thefirst pulp layer 15 containing these additives as the outermost layer tohave a surface tension of 10 dyn/cm or less and a water repellency ofR10 (JIS P 8137). Further, incorporating a particulate or fibrousthermoplastic synthetic resin to the first pulp slurry imparts abrasionresistance to the first pulp layer 15 to suppress fluffing and the like.The degree of abrasion resistance is preferably 3H or higher in terms ofpencil hardness (JIS K 5400).

[0056] According to the present embodiment, a desired characteristic ofa certain additive or pulp fiber can thus be manifested by incorporatingsuch an additive, etc. into only a specific layer where thecharacteristic is to be manifested more efficiently. This provides anadvantage that the amount of the additive, etc. can be minimizedcompared with the amount as required for a single-layered pulp moldedarticle.

[0057] The present invention is not limited to the above-describedembodiment. For example, while in the above embodiment the pulp slurriesand the diluting fluid are fed into the cavity through the piping systemshown in FIG. 1, each of the pulp slurries and the diluting fluid may beseparately fed to the cavity through the individual pipe lines.

[0058] The means for lowering the pulp slurry concentration in thecavity in the initial stage or the final stage of pulp layer formationin the papermaking step is not limited. For example, a pulp slurryhaving a low concentration may be fed in the initial stage of pulp layerformation and then switched over to a pulp slurry having a normalconcentration (the set concentration) when a predetermined feed amountis reached. Likewise a switch-over may be made from a pulp slurry havinga normal concentration (set concentration) to a pulp slurry having alower concentration in the final stage of pulp layer formation.

[0059] In order to increase the suction and dewatering efficiency, warmwater can be used for a fluid of the pulp slurries. In this case, warmwater of 35 to 90° C. is preferable, particularly 45 to 80° C. ispreferable, is more preferable.

[0060] The method of producing a pulp molded article according to thepresent invention is applicable to the manufacture of molded articleshaving a single-layer structure or a three- or more-layered multilayerstructure.

[0061] For example, the method is applicable to the manufacture of amolded article having the layer structure shown in FIG. 3. It is alsoapplicable to the manufacture of a molded article having the structureshown in FIG. 4(a), in which another first pulp layer 15′ is formed onthe side of the second pulp layer 17 shown in FIG. 3, and a mixed layer16′ whose composition continuously varies from the composition of thesecond pulp layer 17 to that of the first pulp layer 15′ is formedbetween the second pulp layer 17 and the first pulp layer 15′, therebymaking up a 5-layered structure of which the innermost layer and theoutermost layer have the same composition. In this embodiment, the firstpulp layers 15 and 15′ may be made of pulp having a high degree ofwhiteness, while the second pulp layer 17 may be made of pulp having alow degree of whiteness, such as pulp of used paper, to provide a moldedarticle which has a highly white appearance and a low price. It is alsopossible that a third pulp layer 21 different in composition from eitherof the second pulp layer 17 and the first pulp layer 15 is formed on theside of the second pulp layer 17 shown in FIG. 3, and a mixed layer 20whose composition continuously varies from the composition of the secondpulp layer 17 to that of the third pulp layer 21 is formed between thesecond pulp layer 17 and the third pulp layer 21 thereby making up alayer structure having 5 layers in total as shown in FIG. 4(b). In thiscase, a multilayer molded article having various materials can beproduced. In the production of molded articles having a single-layer ora three- or more-layer structure, too, the concentrations of the pulpslurries fed into the cavity are preferably set within a range of 0.1 to6% by weight, particularly 0.5 to 3% by weight.

[0062] After the papermaking step, a plastic layer, a coating layer, andthe like may be provided on the outer side and/or the inner side of themolded article to enhance the strength of the molded article or toprevent leakage of the contents, or for the purpose of decoration.

[0063] A reinforcing member made of plastics, etc. may be applied on theportion of the molded article to which a load is imposed, (for example,the opening or the bottom portion.) Otherwise, a part of these portionsmay be formed of plastics, etc.

[0064] The present invention is also applicable to the production ofsubstantially rectangular parallelepipedal cartons of which the openingand the body have substantially the same cross-sectional contour.

[0065] The present invention is applicable to the production of not onlyhollow containers for keeping things in but various shapes such asornaments.

[0066] Where two or more kinds of pulp slurries having differentcompositions are injected into the cavity in succession, each followedby suction dewatering through the suction passageways of the papermakingmold, pulp layers made of the solid component of each pulp slurry can beformed successively without forming a mixed layer. While a pulp slurryis being injected, dewatering may be carried out merely by drainagethrough an opened drain valve. In this case, the slurry is dewatered bysuction after completion of the injection of the pulp slurry. Thedewatering using the pressing member may be replaced with aerationdewatering by feeding air, steam, etc. from the inside of the moldedarticle.

[0067] The present invention is suited to the method in which splitshaving suction passageways are assembled into a papermaking mold, and apulp slurry is injected downward into the cavity of the mold as in theaforementioned embodiment. The present invention is also applicable to amethod in which a split of the papermaking mold is immersed in a tankfilled with the pulp slurry to supply the pulp slurry into the cavity ofthe mold. The present invention is also applicable to a method in whicha split of the papermaking mold having suction passageways is placedwith its papermaking surface up, and an outer frame surrounding at leastthe papermaking surface of the split is set up on the papermaking moldwith liquid tightness to form a space, in which a prescribed amount of apulp slurry is poured and sucked through the suction passageways to forma molded article on the papermaking surface.

[0068] In Examples 1 to 4 and Comparative Example 1, molded articleswere produced by using the papermaking mold and the feed system shown inFIG. 1. Test pieces were cut out of the resulting molded articles, andan average thickness, the largest thickness, the smallest thickness, thelargest to the smallest thickness ratio, and a compressive strength(maximum strength) of the test pieces were measured. The results areshown in Table 1. Table 1 also furnishes the injection volume and theinjection time of the diluting fluid (water) in Examples and ComparativeExamples.

EXAMPLE 1

[0069] A molded article was produced by using a pulp slurry having thecomposition described later. Water was injected to dilute the pulpslurry in the cavity in the initial stage and the final stage of pulplayer formation in the papermaking step according to the time chartshown in FIG. 5.

[0070] Prior to injecting the pulp slurry, 0.5 liter (0.25 l/sec) ofambient temperature water (tap water at 5 to 20° C., hereinafter thesame) as a diluting fluid was injected into the cavity (capacity: 1liter). The pulp slurry was fed under a pressure of 0.1 MPa. The cavitywas then sucked through the suction passageways to dewater the pulpslurry and deposit pulp on the papermaking surface. After 4.5 liters ofthe pulp slurry was injected, 0.5 liter (0.25 l/sec) of ambienttemperature water was injected into the cavity as a diluting fluid. Apressing member made of an elastic material was inserted into theresulting pulp preform, and air was introduced into the pressing memberunder a pressure of 0.3 MPa to press the pulp preform onto the innerwall of the cavity to further dewater the preform.

[0071] The papermaking mold was opened to take out the pulp preform,which was fitted into a drying mold having the same inner profile as thepapermaking mold. A pressing member made of an elastic member wasinserted into the pulp preform fitted in the drying mold, and air wasintroduced into the pressing member under a pressure of 1 MPa thereby topress the pulp preform to the inner wall of the cavity. In this state,the drying mold was heated to 220° C. to dry the pulp preform. After thepulp preform dried sufficiently, the drying mold was opened to take outa bottle-shaped molded article. TABLE 1 Example Comparative Example 1 23 4 1 Layer structure A A A A A Water for initial Volume (l) 0.5 1.252.5 5.0 0 stage dilution Time (sec) 2 5 10 20 0 Water for final Volume(l) 0.5 1.25 2.5 5.0 0 stage dilution Time (sec) 2 5 10 20 0 Averagethickness (mm) 0.68 0.63 0.63 0.61 0.70 Largest thickness (mm) 1.07 0.850.88 0.82 1.17 Smallest thickness (mm) 0.39 0.39 0.44 0.46 0.38Largest/smallest thickness 2.74 2.15 2.02 1.78 3.09 ratio Compressivestrength (N) 431 474 451 491 301

EXAMPLES 2 to 4

[0072] Molded articles were produced in the same manner as in Example 1,except for changing the injection volume and injection time of water asa diluting fluid in the papermaking step as shown in Table 1.

COMPARATIVE EXAMPLE 1

[0073] A molded article was produced in the same manner as in Example 1,except that water was not injected, and the pulp slurry was not diluted.

[0074] Evaluation of Thickness Unevenness

[0075] The thickness of the upright wall (except the threaded part) ofthe molded article was measured at 8 positions selected in the verticaldirection with a micrometer. The thickness unevenness was evaluated fromthe largest thickness, the smallest thickness, and the largest to thesmallest thickness ratio.

[0076] Measurement of Compressive Strength

[0077] A cylindrical member having a screw thread on its outerperipheral surface was press fitted over the neck of the resultingbottle-shaped molded article. The molded article was filled with 79 g ofa powder (Funmatsu Wide Hiter, a production of Kao Corp.), and a cap wasscrewed on. The molded article and the contents were set on acompressive strength measuring instrument (RTA-500, supplied by OrientecCompany), and the compressive strength was measured at a cross headspeed of 20 mm/min.

[0078] As is apparent from the results shown in Table 1, it wasconfirmed that the molded articles prepared in Examples 1 to 4 (theproducts of the present invention) have smaller thickness unevenness inthe vertical direction and higher compressive strength than those ofComparative Example 1.

INDUSTRIAL APPLICABILITY

[0079] According to the present invention, a pulp molded article withreduced thickness unevenness in the vertical direction can be produced.

1. (Amended) A method of producing a pulp molded article which includesa papermaking step comprising joining splits each having suctionpassageways into a papermaking mold, feeding a pulp slurry into thecavity of the papermaking mold, and sucking the pulp slurry through thesuction passageways to form a pulp layer on the inner surface of thepapermaking mold, wherein a fluid for diluting the pulp slurry is fedinto the cavity during the pulp slurry is remaining in the cavity, andthe concentration of the pulp slurry in the cavity in the final stage ofpulp layer formation in the papermaking step is lowered.
 2. The methodof producing a pulp molded article according to claim 1, wherein a fluidfor diluting said pulp slurry is fed into said cavity at least beforestarting the feed of the pulp slurry into the cavity and/or aftercompletion of said feed.
 3. The method of producing a pulp moldedarticle according to claim 1, wherein said pulp slurry to be fed intosaid cavity is at least two pulp slurries different in composition, andthe start of feeding the first pulp slurry of said pulp slurries isfollowed by feeding the second pulp slurry of said pulp slurries. 4.(Amended) A method of producing a pulp molded article which includes apapermaking step comprising joining splits each having suctionpassageways into a papermaking mold, feeding a pulp slurry into thecavity of the papermaking mold, and sucking the pulp slurry through thesuction passageways to form a pulp layer on the inner surface of thepapermaking mold, wherein at least two pulp slurries of differentcomposition are fed into the cavity, the start of feeding the first pulpslurry of said pulp slurries is followed by feeding the second pulpslurry of said pulp slurries, and a fluid for dilution and agitation isfed into the cavity at least the final pulp slurry of said pulp slurriesfed into the cavity is remaining in the cavity.
 5. (Deleted)
 6. Themethod of producing a pulp molded article according to claim 1, whereina fluid for diluting said pulp slurry is fed through a pipe system forfeeding said pulp slurry.
 7. The method of producing a pulp moldedarticle according to claim 4, wherein a fluid for diluting and agitatingsaid final pulp slurry is fed into the cavity after completion of thefeed of said final pulp slurry into the cavity and while the pulp slurryremains in the cavity.